Poor flowability of NCM cathode powder leads to inconsistent feeding during grinding/classification, bridging in hoppers, uneven electrode coating, unstable tap density and batch-to-batch variation of particle size distribution. NCM powder flowability is mainly affected by fine particle content, residual lithium, moisture, static charge, particle morphology and agglomeration state. Based on JACAN NCM processing technology from ncm-mill.com, the following integrated methods can effectively boost NCM powder flowability.
1. Optimize particle size distribution and reduce excess ultra-fine fines
Excessive submicron fines increase specific surface area and inter-particle adhesion, which is the primary cause of poor powder flow.
- Control the span of PSD within a reasonable narrow range. Avoid over-grinding that generates massive ultra-fine particles.
- Use precision air classification to cut off excess fine fractions and maintain a balanced particle gradation. A suitable mix of medium and fine particles reduces void fraction and inter-particle friction.
- Keep Dmax under control to avoid oversized hard agglomerates which disrupt steady powder movement.
2. Lower surface residual lithium and control raw material moisture
High residual lithium on NCM particle surfaces creates sticky lithium hydroxide and lithium carbonate when contacting trace moisture, increasing particle adhesion.
- Use qualified calcined NCM feedstock with low residual lithium content.
- Strictly control raw material moisture below 0.1%. Maintain low dew point in the whole inert gas processing loop to prevent water adsorption. Even tiny moisture will degrade flowability rapidly.
3. Eliminate static electricity accumulation
Fine NCM particles generate static charges during pneumatic conveying and grinding. Static attraction makes particles cling together and stick to equipment walls.
- Implement full equipment grounding for the grinding chamber, classifier, cyclone, filter and all pipelines.
- Adopt conductive ceramic or conductive PU linings to dissipate static without introducing metal impurities.
- Optimize nitrogen gas dew point properly to help static dissipation, while not introducing excess moisture.
4. Adjust particle morphology and reduce agglomeration
Rounded, less irregular particles slide more easily; fluffy soft agglomerates severely hurt flow performance.
- Adopt gentle de-agglomeration instead of violent impact crushing to retain the original spherical-like primary particle shape. Avoid producing sharp broken particle surfaces.
- Optimize grinding and classification parameters to break soft calcined agglomerates and suppress re-agglomeration during processing. Prevent the formation of large loose agglomerates.
5. Optimize process atmosphere and temperature control
High temperature can activate surface lithium compounds and trigger re-agglomeration. Ambient oxygen and moisture worsen surface side reactions.
- Operate the grinding-classification circuit under sealed closed-loop nitrogen atmosphere, keeping low oxygen and low dew point.
- Install temperature interlock protection to restrict powder outlet temperature. Prevent thermal-induced particle adhesion and caking.
6. Auxiliary handling and equipment design for powder transfer
Even good powder can lose flowability with poor equipment geometry.
- Design hoppers and silos with smooth walls and proper cone angles to avoid powder bridging and rat-holing.
- Apply auxiliary mild vibration or gas fluidization in feeding sections for consistent powder feeding, without breaking primary particles.
- Use smooth, ceramic-lined pipelines to reduce powder adhesion and dead zones.
Improving NCM powder flowability is achieved through multi-factor control: tuning PSD to reduce ultra-fine fines, lowering residual lithium and moisture, static dissipation, preserving favorable particle morphology, inert low-dew-point atmosphere and optimized powder transfer equipment. Well-improved flowability stabilizes feeding in dry grinding lines, guarantees consistent tap density and supports uniform cathode coating for lithium battery manufacturing.
